|The Blue Butterfly|
|Season 4, Episode 14|
|Air date||February 6, 2012|
|Written by||Terence Paul Winter|
|Directed by||Chuck Bowman|
Castle gets a hold of a diary that was written in the 1940s, and tries to solve a modern day crime through the information in it. Every time he reads it he flashes back to the '40s, with the principal cast playing characters in the diary.
- Nathan Fillion as Richard Castle
- Stana Katic as Detective Kate Beckett
- Jon Huertas as Detective Javier Esposito
- Seamus Dever as Detective Kevin Ryan
- Tamala Jones as Dr. Lanie Parish
- Penny Johnson Jerald as Captain Victoria Gates (credit only)
- Molly Quinn as Alexis Castle
- Susan Sullivan as Martha Rodgers
- Mark Pellegrino as Tom Dempsey / Tom Dempsey III
- Chad Everett as Jerry Maddox / old Joe
- Ellen Geer as Viola Maddox / old Vera
- Patrick Cassidy as Clyde Belasco
- Zahn McClarnon as Ray Horton
- Lorin McCraley as West Side Wally
- Andrea Grano as Stan's ex-wife
- Adam Bay as Leonard
- Sarah Lilly as Luella McManus
- Darin Toonder as Frankie
- Jared Ward as Bartender
- Castle: It happened backstage, right upstairs. They were stealing a moment together which was dangerous because she was Dempsey’s girl. As they stared into each other’s eyes, Kate’s heart quickened...
- Beckett: Did you just say Kate? Are you picturing the PI as you and me as a gangster’s moll?
- Castle: What?! No! And I didn't say Kate, I said fate. Fate’s heart quickened. I was being poetic. God. Anyway…
- Betsy (about Joe): You better wise up, Vera. Dempsey will have you butchered if he finds out. I mean, he's a hell of a smoocher and all but, damn it, girl, is this yum-yum really worth it?
- Vera: He's the cream in my coffee.
- Betsy: You two are a walking fairy tale, good Lord.
- "I Can't Give You Anything But Love" - Louis Armstrong
- "Comes Love - Unreleased" - Tamala Jones (sing as Besty Sinclair) - Arranged by Robert Duncan
- This marks the first time that actress Tamala Jones (Lanie Parish) has sung in public.
- The title evokes such classic PI tales as "The Maltese Falcon".
- Beckett's 1940s alter ego is named Vera. "Vera" was the name of Jayne Cobb's favorite gun on Firefly, Nathan Fillion's old show.
- ↑ Credited at the end of episode as Frankie but near the end of episodes also referred by his full name Francis Benjamin Huntsacker
- ↑ Castle's Tamala Jones singing Comes Love video at YouTube